Frédéric Cayrel
François Rabelais University
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Featured researches published by Frédéric Cayrel.
Applied Physics Letters | 2010
X. Song; Jean-François Michaud; Frédéric Cayrel; Marcin Zielinski; Marc Portail; Thierry Chassagne; Emmanuel Collard; Daniel Alquier
In this paper, we demonstrate the high electrical activity of extended defects found in 3C–SiC heteroepitaxially grown layer on (100) silicon substrates. Cross-sectional scanning transmission electron microscopy analysis was performed to reveal the defects while scanning spreading resistance microscopy aimed to study their electrical behavior. Using this technique, complete layer resistance cartography was done. The electrical activity of the extended defects in 3C–SiC was clearly evidenced. Furthermore, the defect activity was estimated to be higher than that of heavily nitrogen doped (5×1018 cm−3) 3C–SiC layer.
RSC Advances | 2015
Charles Opoku; Abhishek Singh Dahiya; Frédéric Cayrel; Guylaine Poulin-Vittrant; Daniel Alquier; Nicolas Camara
The present work demonstrates the production of single crystalline ZnO nanowires (NWs) using the low temperature hydrothermal process and their integration as the active channel material and piezoelectric elements in single NW field-effect transistors (FETs) and functional nanogenerators (NGs), respectively. Even though hydrothermally grown ZnO NWs show high levels of excess free carriers ≫1018 cm−3, we show that an optimized thermal annealing process at just 450 °C in atmospheric air sufficiently reduces this level to around ∼3.7 × 1017 cm−3. The excess free carrier suppression is verified by assessing the field-effect transport behaviour in a single NW FET. The single device is found to exhibit good performance metrics, including low off-state current (pA range), high on-state current (in the 10 s of μA range) and moderate effective mobility (∼10 cm2 V−1 s−1). The functional NGs are based on vertically grown ZnO NWs with ∼7 μm thick polydimethylsiloxane (PDMS) polymer matrix. We show that a NG incorporating annealed ZnO NWs can continuously generate higher output voltages and power compared to a reference device based on as-grown ZnO NWs. This included peak output voltage of ∼109 mV and an output power density of ∼16 μW cm−3. We envisage that this approach of thermal annealing may find practical applications in other areas of hydrothermal ZnO NW research, including high performance NW FETs and piezoelectric energy harvesters.
Nanotechnology | 2015
Charles Opoku; Abhishek Singh Dahiya; Christopher Oshman; Christophe Daumont; Frédéric Cayrel; Guylaine Poulin-Vittrant; Daniel Alquier; Nicolas Camara
The production of large quantities of single crystalline semiconducting ZnO nanowires (NWs) at low cost can offer practical solutions to realizing several novel electronic/optoelectronic and sensor applications on an industrial scale. The present work demonstrates high-density single crystalline NWs synthesized by a multiple cycle hydrothermal process at ∼100 °C. The high carrier concentration in such ZnO NWs is greatly suppressed by a simple low cost thermal annealing step in ambient air at ∼450 °C. Single ZnO NW FETs incorporating these modified NWs are characterized, revealing strong metal work function-dependent charge transport, unobtainable with as-grown hydrothermal ZnO NWs. Single ZnO NW FETs with Al as source and drain (s/d) contacts show excellent performance metrics, including low off-state currents (fA range), high on/off ratio (10(5)-10(7)), steep subthreshold slope (<600 mV/dec) and excellent field-effect carrier mobility (5-11 cm(2)/V-s). Modified ZnO NWs with platinum s/d contacts demonstrate excellent Schottky transport characteristics, markedly different from a reference ZnO NW device with Al contacts. This included abrupt reverse bias current-voltage saturation characteristics and positive temperature coefficient (∼0.18 eV to 0.13 eV). This work is envisaged to benefit many areas of hydrothermal ZnO NW research, such as NW FETs, piezoelectric energy recovery, piezotronics and Schottky diodes.
Applied Physics Express | 2012
H. P. David Schenk; Alexis Bavard; E. Frayssinet; Xi Song; Frédéric Cayrel; Hassan Ghouli; Melania Lijadi; Laurent Naïm; Mark Kennard; Y. Cordier; Daniel Rondi; Daniel Alquier
We report on silicon n-type delta (δ)-doping of gallium nitride (GaN) epitaxial layers grown by metalorganic chemical vapor deposition (MOCVD) on silicon (111) substrates. In a series of group III–nitride epitaxial structures a ~1-µm-thick Si bulk-doped GaN layer is replaced by 100, 50, 10, 5, or 1 Si δ-doped planes. While Si bulk-doping of GaN aggrandizes the in-plane tensile stress and the wafer bow with respect to undoped structures, δ-doping is found to reduce both stress and wafer bow. Two-dimensional carrier sheet densities between 1012 and 1013 cm-2 per δ-doped plane and electron mobilities of 1429 cm2 V-1 s-1 are achieved.
Materials Science Forum | 2009
Olivier Ménard; Frédéric Cayrel; Emmanuel Collard; Daniel Alquier
In this work, Ti/Al bilayer sputtered ohmic contacts on n-type Gallium Nitride films were studied as a function of process parameters such as Ti thickness, surface cleaning procedure or annealing temperature. Epilayers, with doping concentration of 5.8x1018 at.cm-3, were grown on sapphire using AlN buffer layer. Electrical characterizations were made using circular Transfer Length Method (cTLM) patterns with a four probes equipment. Specific Contact Resistance (SCR) was then extracted for all the process conditions. Our results show that surface treatment is not a critical step in the ohmic contact process while annealing temperature has a larger impact. Finally, SCR values of 1x10-5 Ω.cm2 can be reproducibly achieved, which is of high interest for future devices fabrication using this material.
Journal of Applied Physics | 2005
P. Petrik; M. Fried; T. Lohner; O. Polgár; J. Gyulai; Frédéric Cayrel; Daniel Alquier
Cavities created by He implantation with a dose of 5×1016cm−2 and energy of 40keV into single-crystalline silicon and annealing at 650–1000°C for 15–60min were characterized by multiple angles of incidence spectroscopic ellipsometry. Optical models of increasing complexity were developed assuming the cavity layer either to be homogeneous, or to have a Gaussian profile, or sublayers with independently fitted cavity ratios. Cavity profiles of different annealing conditions were compared and cross-checked by transmission electron microscopy. A strategy for the ellipsometric evaluation was proposed to reduce the computation time and the probability of getting in local minima using complex models with numerous parameters. High sensitivity on the angle of incidence was found, and the choice and the determination of the angle of incidence were discussed.
IEEE Electron Device Letters | 2012
Gaël Gautier; Marie Capelle; Jérôme Billoué; Frédéric Cayrel; Patrick Poveda
For the first time, inductors were integrated on porous silicon carbide to study the effect of this substrate on radio-frequency (RF) performances. n-Type heavily doped 4H-SiC substrates were anodized in an HF-based electrolyte to produce 6- and 15-μm-thick porous layers. An improvement of the quality factor was demonstrated on porous SiC with regard to SiC bulk. This promising result shows the decrease of substrate losses at the high frequencies with the porous SiC substrate. Thus, porous SiC could have an interest for the integration of RF power devices.
2010 WIDE BANDGAP CUBIC SEMICONDUCTORS: FROM GROWTH TO DEVICES: Proceedings of the E‐MRS Symposium* F* | 2010
A.E. Bazin; Jean-François Michaud; Frédéric Cayrel; Marc Portail; Thierry Chassagne; Marcin Zielinski; Emmanuel Collard; Daniel Alquier
3C‐SiC, the only polytype which can be heteroepitaxially grown on large diameter silicon substrates, is a promising material to achieve power Schottky diodes. To carry out such diodes, high quality ohmic contacts are required. In this work, ohmic contacts were investigated on in situ highly n‐doped 3C‐SiC epilayers grown on (100) cheap silicon substrates. Different metals such as nickel, titanium, aluminum and gold were used to carry out the contacts. Classical circular Transfert Length Method (c‐TLM) structures were prepared to evaluate the specific contact resistance. Ni and Ti‐Ni contacts were annealed between 950° C and 1050° C while Al and Ti‐Au contacts were annealed between 300° C and 600° C. The specific contact resistance was then determined by using c‐TLM patterns. For each investigated contact, the best specific contact resistance values obtained are lower than 2×10−5Ω⋅cm2, even consecutively to a low temperature annealing.
Materials Science Forum | 2012
A. Stavrinidis; G. Konstantinidis; M. Kayambaki; Frédéric Cayrel; Daniel Alquier; Zhuo Gao; Konstantinos Zekentes
The process technology for the fabrication of 4H-SiC Static Induction Transistors (SITs) has been developed. Conventional contact UV lithography and self-aligned techniques have been employed. Al-outdiffusion following Rapid Thermal Annealing (RTA) has been determined as the cause for the increased reverse leakage and early forward turn-on of the gate-source junction. The fabricated transistors, exhibited a specific RON value in the region of 2mΩ•cm2 and 80 V turn-off voltage.
Solid State Phenomena | 2007
O. Marcelot; A. Claverie; Daniel Alquier; Frédéric Cayrel; Wilfried Lerch; Silke Paul; Leonard M. Rubin; Vito Raineri; Filippo Giannazzo; H. Jaouen
We have designed a set of experiments in which a controlled supersaturation of vacancies can be maintained constant during annealing of a boron implant. In presence of voids, a remarkable reduction of boron diffusivity is observed and, for low fluence B implantation, TED can be totally suppressed. We show that the presence of nanovoids in the B implanted region is not a prerequisite condition for the reduction of B diffusivity. Large voids located at more than 100 nm apart from the B profile still show the same effect. Small voids can also be used to increase the activation of boron. All these results are consistent with the hypothesis that, during annealing, vacancies are injected from the voids region towards the Is rich region in the implanted region where they massively recombine. Finally, we show that BICs cannot be simply dissolved by injecting vacancies into the region where they stand.